The short answer
If you have time for only one night in the north-west, Rabat is usually the better stay and Casablanca the better half-day. Rabat has a navigable UNESCO medina, the Kasbah of the Udayas and a relaxed pace with little touting. Casablanca has the Hassan II Mosque. The two are about an hour apart, so seeing both is easy.
In more detail
Casablanca's strength is practical: Mohammed V Airport is there, so an overnight before or after a flight lets you see the mosque without an extra transfer. Its food scene and Corniche reward an evening.
Rabat is the capital, green and calm. The Kasbah of the Udayas, a 12th-century fortress above the Bou Regreg estuary with whitewashed, blue-based houses and an Andalusian garden, is one of the loveliest corners of the country. The Hassan Tower, the unfinished minaret begun under the same sultan who built the Koutoubia in Marrakech, and the Chellah necropolis are both close by.
A good plan is to land in Casablanca, spend a night and see the mosque, take the fast train to Rabat for two nights, then continue south to Marrakech or north to Tangier. Rabat to Marrakech is about 3h30 by road.
Good to know
- The Chellah is best in spring, when the storks are nesting.
- Rabat's medina is one of the least pressured in Morocco.
- Trains between the two cities are frequent.